U.S. patent application number 10/229077 was filed with the patent office on 2003-06-19 for heat-dissipating substrate, method for making the same, and semiconductor device including the same.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Fukui, Akira, Omachi, Masahiro.
Application Number | 20030113578 10/229077 |
Document ID | / |
Family ID | 19090163 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030113578 |
Kind Code |
A1 |
Omachi, Masahiro ; et
al. |
June 19, 2003 |
Heat-dissipating substrate, method for making the same, and
semiconductor device including the same
Abstract
A heat-dissipating substrate is made of a composite material
comprising a first composition primarily composed of aluminum and a
second composition primarily composed of silicon carbide and/or
silicon The heat-dissipating substrate has a recess in one of its
main faces. The main faces have fine unevenness, and the maximum
amplitude of the fine unevenness in the depth direction of a main
face is smaller than the maximum length in the depth direction of
composite particles comprising the first composition and the second
composition or particles of the second composition, the particles
being exposed at the surface of the main face.
Inventors: |
Omachi, Masahiro;
(Itami-shi, JP) ; Fukui, Akira; (Itami-shi,
JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
|
Family ID: |
19090163 |
Appl. No.: |
10/229077 |
Filed: |
August 28, 2002 |
Current U.S.
Class: |
428/687 ;
257/E23.112 |
Current CPC
Class: |
H01L 2924/01079
20130101; H01L 2924/16152 20130101; Y10T 428/12993 20150115; H01L
2224/73253 20130101; Y10T 428/12389 20150115; H01L 2924/01019
20130101; H01L 2924/3511 20130101; H01L 2924/16195 20130101; H01L
23/3733 20130101; H01L 2924/15311 20130101; H01L 2924/01078
20130101; H01L 2224/16 20130101; H01L 2224/73253 20130101; H01L
2924/16152 20130101 |
Class at
Publication: |
428/687 |
International
Class: |
H01L 025/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2001 |
JP |
263401/2001 |
Claims
What is claimed is:
1. A heat-dissipating substrate made of a composite material
comprising: a first composition primarily composed of aluminum; and
a second composition primarily composed of silicon carbide and/or
silicon, wherein the heat-dissipating substrate has a recess in one
of its main faces, and the maximum amplitude in the depth direction
of fine unevenness excluding the recess in the surface of a main
face is smaller than the maximum length in the depth direction of
composite particles comprising the first composition and the second
composition or particles of the second composition, the composite
particles and the particles being exposed at the surface of the
main face.
2. A heat-dissipating substrate according to claim 1, wherein the
roughness Ra of the two main faces excluding the recess is in the
range of 0.2 to 2 .mu.m in terms of roughness Ra defined in JIS B
0651.
3. A heat-dissipating substrate according to claim 1, wherein the
main faces excluding the recess exhibit gray or light gray color
without metallic luster.
4. A heat-dissipating substrate according to claim 1, wherein the
first composition in the composite material is in the range of 55
to 96 percent by mass.
5. A heat-dissipating substrate according to claim 1, wherein the
composite particles composed of the first composition and the
second composition and the particles composed of the second
composition have an average particle size in the range of 5 to 40
.mu.m, respectively.
6. A heat-dissipating substrate according to claim 1, wherein the
ratio of the maximum thickness t (mm) between the two main faces to
the area A (mm.sup.2) of a main face is 0.002 or less.
7. A heat-dissipating substrate according to claim 1, wherein the
curvature of the heat-dissipating substrate in the thickness
direction is 0.05 mm or less.
8. A method for making a heat-dissipating substrate, comprising: a
step of preparing a composite material comprising a first
composition primarily composed of aluminum and a second composition
primarily composed of silicon carbide and/or silicon; a first
etching step of forming a recess in a main face of the composite
material by chemical etching; and a second etching step of forming
fine unevenness except for the recess on main faces by chemical
etching, such that the maximum amplitude of the fine unevenness in
the depth direction of a main face is smaller than the maximum
length in the depth direction of the composite particles comprising
the first composition and the second component or the particles of
the second composition, the composite particles and the particles
being exposed at the surface of the main face.
9. A method for making heat-dissipating substrates according to
claim 8, wherein the composite material is prepared in a sheet form
for making a plurality of heat-dissipating substrates, and the
recesses are formed at corresponding positions of the
heat-dissipating substrates in the first etching step, allowing a
frame having a small thickness to be formed around each of the
heat-dissipating substrates so as to cause the heat-dissipating
substrates to be separated at the frame.
10. A method for making the heat-dissipating substrate according to
claim 8, wherein the chemical etching in the first etching step is
performed with an alkaline or acidic aqueous etching solution
containing 30 to 50 percent by mass of etchant.
11. A method for making the heat-dissipating substrate according to
claim 8, wherein the chemical etching in the second etching step is
performed with an alkaline or acidic aqueous etching solution
containing 3 to 30 percent by mass of etchant.
12. A method for making heat-dissipating substrates according to
claim 8, wherein the chemical etching in the first etching step or
the second etching step is performed with the alkaline or acidic
aqueous etching solution containing inorganic copper salt or
chloride wherein the total etchant concentration in the solution is
in the range of 3 to 50 percent by mass.
13. A method for making the heat-dissipating substrate according to
claim 8, wherein the chemical etching in the first etching step or
the second etching step is performed with the alkaline or acidic
aqueous etching solution containing hydrogen fluoride.
14. A semiconductor device comprising the heat-dissipating
substrate according to claim 1.
15. A semiconductor device comprising the heat-dissipating
substrate according to claim 2.
16. A semiconductor device comprising the heat-dissipating
substrate according to claim 3.
17. A semiconductor device comprising the heat-dissipating
substrate according to claim 4.
18. A semiconductor device comprising the heat-dissipating
substrate according to claim 5.
19. A semiconductor device comprising the heat-dissipating
substrate according to claim 6.
20. A semiconductor device comprising the heat-dissipating
substrate according to claim 7.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to heat-dissipating substrates
suitable for semiconductor devices. In particular, the present
invention relates to a heat-dissipating substrate comprising a
composite material containing a first composition primarily
composed of aluminum and a second composition primarily composed of
silicon carbide and/or silicon, a method for making the
heat-dissipating substrate, and a semiconductor device including
the heat-dissipating substrate.
[0003] 2. Description of the Background Art
[0004] Recently, the integration density of semiconductor devices
has increased markedly, and heat generated in the semiconductor
devices has also increased exponentially. Thus, heat-dissipating
substrates used in semiconductor devices must have high heat
dissipation and satisfactory matching of thermal expansion
coefficient with semiconductor devices and components for the
semiconductor devices.
[0005] Furthermore, lighter, thinner, and more compact
semiconductor devices are developed; hence, heat-dissipating
substrates must be thinner and more compact. Also, heat-dissipating
substrates have been required to have various complicated shapes,
and these heat-dissipating substrates need to be produced with high
dimensional precision and low cost.
[0006] A known material for such heat-dissipating substrates is a
composite material comprising a metal having a low thermal
expansion coefficient and a high thermal conductivity, i.e.,
tungsten (W) or molybdenum (Mo), and another metal having a high
thermal conductivity, i.e., copper (Cu). However, the W-Cu and
Mo-Cu composite materials are expensive and heavy. When a
heat-dissipating substrate made of such a known composite material
is mounted onto a plastic motherboard, the motherboard and ball
grid are easily deformed or damaged.
[0007] Under such circumstances, light ceramic materials having
high thermal conductivity such as aluminum nitride (AlN) and
silicon carbide (SiC) have been developed as materials for
heat-dissipating substrates. However, ceramic materials have a
disadvantage of high process cost since they cannot be easily
processed. Countermeasure materials are aluminum (Al) and its
alloy, which have high thermal conductivity and are light; however,
these have low hardness and are easily damaged.
[0008] A variety of Al-based alloys and composite materials have
been investigated. For example, a composite material of Al and
silicon (Si) or a composite material of Al and a ceramic having
high thermal conductivity is used for a heat-dissipating substrate.
For example, Japanese Examined Patent Application Publication No.
63-16548 discloses a composite material of Al and Si (Al-Si
composite material). Japanese Unexamined Patent Application
Publication Nos. 1-501489, 2-243729, 9-157773, 10-280082, and
10-335538 disclose composite materials of Al and SiC (Al-SiC
composite materials). Composite materials containing Al, Si, and
SiC are also known.
[0009] However, since these composite materials contain hard SiC
and Si particles, much time is required for finishing processes
such as cutting and grinding, and high load is applied to the
processing tools, which results in quick wear of the tools. Such
high load applies considerable stress to the surfaces of the
composite materials and causes deformation of the composite
materials such as curvature. As described above, thinner substrates
have been developed recently. Such thinner substrates are easily
deformed by high load during the finishing process. Since both soft
Al particles and hard SiC particles are present in the processed
surface, the hard particles are readily scratched off by processing
tools and the resulting cavities are filled with deformed Al
particles. Furthermore, the surfaces processed with worn tools
become more uneven and have low dimensional accuracy.
[0010] Japanese Unexamined Patent Application Publication No.
10-280082 discloses a method for making an Al-SiC composite
material having a predetermined shape without processing such as
cutting and grinding. In this method, a green compact having a
shape substantially similar to the final shape is prepared, and
surfaces of the green compact are covered with specific layers of
silicon oxide or the like to prevent liquation of Al after firing.
However, the formation of the specific layers on the surfaces of
the compact is very troublesome.
[0011] In a thin metal substrate composed of Cu or Al, a shallow
recess for mounting a semiconductor device is generally formed by
chemical etching or corrosion. For example, WO99/0959 discloses an
example of chemical etching for making a multichip module. However,
chemical etching is predominantly applied to soft metal
materials.
[0012] Japanese Unexamined Patent Application Publication No.
10-42579 discloses etching of Al-Si and Al-SiC materials for
sliders, which are quite different from semiconductor devices. The
abrasion resistance of the slider is improved by causing hard
particles to protrude 2 .mu.m or less from the surface by slightly
etching the Al matrix after finish-machining the surface by cutting
or polishing. This technology, however, does not take account of
deformation of the material during cutting and polishing.
[0013] Various types of semiconductor packages for higher
performance and advanced capabilities are developed. For example,
packages of flip-chip mounting types shown in FIGS. 7 and 8 are
employed for increased I/O terminals. In these drawings, reference
numerals 1a and 1b denote heat-dissipating substrates, reference
numeral 2 denotes a semiconductor device mounted on the
heat-dissipating substrate, reference numeral 3 denotes a
multichip-type wiring layer, reference numeral 4 denotes a ball
grid (connection terminal). The heat-dissipating substrate 1a shown
in FIG. 7 constitutes a lid whose peripheral frame is directly
connected with the wiring layer 3. The heat-dissipating substrate
1b shown in FIG. 8 is of a flat plate and the heat-dissipating
substrate 1b and the wiring layer 3 are hermetically sealed with a
stiffener 5.
[0014] In compliance with the requirement of high performance,
packages of flip-chip type, the number of the wiring layers 3 is
increased. On the other hand, since the total thickness of the
package is specified by a JEDEC (Joint Electron Device Engineering
Council) standard, the heat-dissipating substrates 1a and 1b must
be thinner so that the package complies with the standard. However,
the above-described Al-SiC and Al-Si heat-dissipating substrates
easily undergo deformation such as curvature as the thickness is
reduced by cutting or grinding. As for the lid-type
heat-dissipating substrate 1a shown in FIG. 7, in particular, it is
difficult to further reduce the thickness thereof while maintaining
high dimensional accuracy.
[0015] When the heat-dissipating substrate is used in a package,
its product name and lot number are printed on a surface of the
heat-dissipating substrate. Thus, the surface must be conditioned
so that the print is clear. However, identification of printed data
has been difficult in the case of the Al-SiC and Al-Si composite
materials, because they exhibit dark or low gray metallic luster,
although the color varies depending on the composition of the
materials.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is to provide a thin
heat-dissipating substrate which comprises an Al-based composite
material composed of Al-SiC, Al-Si, or the like and which does not
undergo deformation such as curvature and has a surface that allows
data printed thereon such as a product code and lot number to be
clearly identified.
[0017] A heat-dissipating substrate according to the present
invention is made of a composite material comprising a first
composition primarily composed of aluminum and a second composition
primarily composed of silicon carbide and/or silicon, and has a
recess in one of the two main faces thereof, in which the maximum
amplitude of the fine unevenness in the depth direction of the
surfaces excluding the recess portion is smaller than the maximum
length in the depth direction of the composite particles comprising
the first composition and the second composition or the particles
of the second composition that are exposed at the surface of the
same main face.
[0018] Preferably, the two main faces have a roughness Ra of 0.2 to
2 .mu.m in terms of the roughness Ra defined in JIS B 0651.
Preferably, the two main faces excluding the recess portion are
gray or light gray without exhibiting metallic luster.
[0019] A method for making a heat-dissipating substrate according
to the present invention comprises the following steps: a step of
preparing a composite material comprising a first composition
primarily composed of aluminum and a second composition primarily
composed of silicon carbide and/or silicon; a first etching step of
forming a recess in one of the main faces of the composite material
by chemical etching; and a second etching step of forming fine
unevenness on the main faces by chemical etching such that the
maximum amplitude of the fine unevenness in the depth direction of
a main face is smaller than the maximum length in the depth
direction of composite particles composed of the first composition
and the second composition or particles composed of the second
composition, which particles are exposed at the surface of the main
face.
[0020] In the method of making a heat-dissipating substrate
according to the invention, the chemical etching in the first
etching step is performed with an alkaline or acidic aqueous
etching solution containing 30 to 50 percent by mass of etchant and
the chemical etching in the second etching step is performed with
an alkaline or acidic aqueous etching solution containing 3 to 30
percent by mass of etchant. Preferably, the second alkaline or
acidic aqueous etching solution further contains another etchant of
an inorganic copper salt or chloride wherein the total etchant
concentration in the solution is in the range of 3 to 50 percent by
mass. The above-mentioned alkaline or acidic aqueous etching
solutions may further contain hydrogen fluoride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic cross-sectional view of a
heat-dissipating substrate according to the present invention.
[0022] FIG. 2 is an schematic plan view of a composite material
sheet for preparing a number of heat-dissipating substrates.
[0023] FIG. 3 is a schematic surface profile of fine unevenness on
a main face of the heat-dissipating substrate according to the
present invention.
[0024] FIG. 4 is a profile curve of the surface unevenness shown in
FIG. 3.
[0025] FIG. 5 shows a surface unevenness profile of a main face
(excluding a recess portion) of an Al-SiC composite material having
a specific composition.
[0026] FIG. 6 schematically illustrates a method for measuring the
curvature of a substrate
[0027] FIG. 7 is a cross-sectional view of a package using a
lid-type heat-dissipating substrate.
[0028] FIG. 8 is a cross-sectional view of a package using a planar
heat-dissipating substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The composite material that constitutes the heat-dissipating
substrate according to the present invention comprises a first
composition primarily composed of aluminum (Al), namely, pure Al or
an Al alloy, and a second composition primarily composed of silicon
carbide (SiC) and/or silicon (Si), namely, SiC, Si, or a mixture
thereof. The Al alloy of the first composition may contain general
metals defined in JIS H 4040 or JIS H 5202, such as Mg and Si.
[0030] Table I shows the thermal conductivity and thermal expansion
coefficient of pure Al, SiC, and Si. Preferably, the first
composition is composed of pure Al and the second composition is
composed of high-purity SiC or Si to ensure high thermal
conductivity. Preferably, SiC is of crystalline type exhibiting
high thermal conductivity.
1 TABLE I Al SiC Si Thermal Conductivity (W/m .multidot. K) 220 320
140 Thermal Expansion Coefficient (.times.10.sup.-6/.degree. C.) 24
4 4.2
[0031] Referring to FIG. 1, a heat-dissipating substrate 10
according to the present invention has one or more recess 11 on a
main face 10a thereof. Here, a "main face" represents a face on
which a semiconductor device is to be mounted or a face of the
opposite side. The recess 11 may have any desired shape according
to the package design. For example, the recess 11 may have a simple
flat bottom (general lid type) or a waved bottom. The portion
excluding the recess 11 of the main face 10a is a joint frame
portion 12 to which a wiring layer and other components are bonded.
A main face 10b that is opposite to the main face 10a is used as a
face on which marks such as product name and lot number are
printed.
[0032] The recess 11 is formed by chemical etching, as described in
detail below. Furthermore, the surfaces excluding the recess 11 of
the main faces 10a and 10b are subjected to another chemical
etching so as to have fine unevenness of a specific profile. FIG. 3
shows a schematic view of such fine unevenness on the main faces.
In reference to FIG. 3, the numeral 15 indicates a main face of the
heat-dissipating substrate and 16 indicates hard particles exposed
on the surface of the main face 15. The hard particles 16 are
composite particles composed of the first composition and the
second composition or particles composed of the second composition
only. The numeral 17 designates the matrix portion composed of the
first composition. In a microscopic view, the surface of the matrix
portion 17 and the top face of each fine particle 16 exhibit fine
unevenness, 17a and 16a, respectively. Also the interface between
the matrix 17 and each fine particle 16 has a fine recess.
[0033] FIG. 4 illustrates a profile of microscopic surface
unevenness at a cross-section orthogonal to the main face 15 in the
case of excluding the recess 11 of the main faces 10a and 10b shown
in FIG. 1. This profile curve corresponds to the surface unevenness
shown in FIG. 3. The maximum amplitude A.sub.max of the unevenness
in the depth direction in FIG. 4 is smaller than the maximum length
D.sub.max of the hard particles 16 in the depth direction in FIG.
3.
[0034] As a result of such a surface profile, the first and second
main faces 10a and 10b are gray or light gray without metallic
luster. Furthermore, the joint frame portion 12 having a surface
state of the above-mentioned profile as a part excluding the recess
11 of the main face 10a has high bonding strength and hence is
superior in reliability of connection with other components
disposed on the heat-dissipating substrate 10.
[0035] Preferably, the surface roughness Ra of the main faces 10a
and 10b is in the range of 0.2 to 2 .mu.m, wherein the surface
roughness Ra is defined in Japanese Industrial Standard (JIS). A
surface with a surface roughness Ra of less than 0.2 .mu.m has
metallic luster, which impairs clearness of printed letters and
tends to decrease the strength of bonding with other components. A
rough surface with a surface roughness Ra exceeding 2 .mu.m tends
to be more blackish, which also impairs clearness of printed
letters. More preferably, the surface roughness Ra is in the range
of 0.5 to 1.2 .mu.m.
[0036] Preferably, the first composition of the composite material
composing the heat-dissipating substrate of the present invention
is in the range of 55 to 96 percent by mass, the balance being the
second composition and inevitable impurities. If the first
composition is less than 55 percent by mass, the etching rate and
thus the efficiency in the formation of the recess tend to
decrease. In a case where the first composition exceeds 96 percent
by mass, the properties of the composite material become
substantially the same as those of pure Al or an Al alloy; the
composite material does not show properties that are industrially
useful. For the same reasons, when the second composition is
composed of SiC only, the first composition is preferably in the
range of 60 to 95 percent by mass, and when the second composition
is composed of Si only, the first composition is preferably 55 to
88 mass percent.
[0037] The composite particles composed of the first composition
and second composition and the particles composed of the second
composition preferably have an average particle size in the range
of 5 to 40 .mu.m and more preferably 10 to 20 .mu.m. If their
average particle size is less than 5 .mu.m, the surface area of the
particles containing large amounts of the second composition
becomes large, so that the etching rate during the formation of the
recess tends to decrease, whereby decreasing the efficiency of
making the recess. If their average particle size exceeds 40 .mu.m,
the amplitude of the unevenness on the main faces excluding the
recess increases, which makes it difficult to obtain a desired
color of the main faces.
[0038] The heat-dissipating substrate having the above
configuration has relatively high size accuracy and can be thinner
than conventional substrates. For example, even when the ratio t/A
of the maximum thickness t (mm) of the substrate between the main
faces to the area A (mm.sup.2) of a main face is 0.002 (mm.sup.-1)
or less, the curvature of the substrate can be reduced to 0.08 mm
or less, and under ideal finishing conditions, to 0.05 mm or
less.
[0039] The heat-dissipating substrate of the present invention has
high rigidity, in addition to a high heat dissipation effect and
high size accuracy; hence, the heat-dissipating substrate may be of
a planar type shown in FIG. 8, of a lid type shown in FIG. 7 or of
a thinner type with a more complicated shape.
[0040] A method for making the heat-dissipating substrate of the
present invention will now be described. A composite material for
the heat-dissipating substrate is prepared by a known method.
Specifically, an Al-SiC or Al-Si composite material is prepared by
an infiltration method, a sintering method, a casting method, or a
combination thereof. Contaminants and an oxide layer on the
surfaces of the resulting composite material are removed by a known
means, such as barrel polishing and shot blasting.
[0041] When the infiltration method is employed in the present
invention, a powder of the second composition and an organic binder
to be added thereto as needed are granulated, and the granular
mixture is molded into a desired shape to form a green compact. The
void volume of the green compact can be adjusted by firing in a
nonoxidizing atmosphere, if necessary, in order to ensure the void
volume for impregnating the first composition. Thereafter, in a
state in which the porous compact is brought into contact with the
first composition, the first composition is melted by heating in a
nonoxidizing atmosphere such that the porous compact is impregnated
with the melted first composition so as to form a composite
material.
[0042] In the case of a sintering method, a powder of the first
composition and a powder of the second composition are mixed
according to the composition of the final product, and an organic
binder may be added thereto as needed, and the mixture may be
granulated. A powder of the mixture is molded into a desired shape,
and the green compact is heated at a temperature above the melting
point of the first composition in a nonoxidizing atmosphere to
liquid-sinter the green compact. A composite material is thereby
prepared.
[0043] In both the infiltration method and the sintering method, a
protective layer may be provided on the porous compact or the green
compact to prevent the first composition from migrating to outer
surfaces. Thus, a net-shape heat-dissipating substrate can be
prepared by simple finishing of the resulting composite
material.
[0044] In the case of casting method, the first composition is
melted in a nonoxidizing atmosphere in a container, and a
predetermined amount of powder of second composition is added
thereto, and the mixture is thoroughly blended to attain uniform
dispersion, and cast into a predetermined shape, and then cooled to
form a composite material. In the above infiltration method, the
first composition is generally 50 percent by mass or less because
it is difficult to maintain the shape of the composite material if
the pore volume of the porous second composition is larger.
Therefore, the sintering method and the casting method that can be
applied without restriction to composition are preferable in the
present invention.
[0045] In the case of an Al-Si composite material, an alternative
method may be employed, in which a powder is prepared by quenching
sprayed molten metal having a desired composition, and the powder
is hot-rolled. In addition various methods are available, depending
on the composition and shape of the substrate material: sintering
may be performed by hot-press, hot casting, or hot hydrostatic
molding, and a hot plastic processing may be performed after these
processes, etc.
[0046] The raw material for the first composition is powder in the
case of the sintering method. In the case of the infiltration
method and the casting method, however, it may be other forms such
as granular, for example. In view of the final thermal
conductivity, the first composition is preferably composed of pure
Al or an Al alloy including minimal other element. The raw material
for the second composition is powder and is preferably composed of
SiC or Si whose purity is as high as possible. Preferably, SiC is
crystalline SiC such as type 6H having high thermal
conductivity.
[0047] The average particle size of the powder for the second
composition is preferably in the range of 5 to 40 .mu.m, and more
preferably 10 to 20 .mu.m As described above, an average particle
size of less than 5 .mu.m results in a decreased etching rate
during the etching process of the composite material for forming
the recess. An average particle size exceeding 40 .mu.m forms
unevenness having large amplitude on the main faces, which results
in difficulty in obtaining the desired tone of color on the main
faces.
[0048] The resulting composite material is subjected to chemical
etching two times, one for forming a recess and the other for
controlling the roughness of the main faces. Specifically, in the
first chemical etching step, a recess having a predetermined
pattern is formed on a part of one of main faces. In the second
chemical etching step, the roughness of the two main faces is
adjusted so that the main faces have desired color and appearance.
The order of the first and second etching steps is not limited.
Masking for the chemical etching may be performed by any known
process such as a photolithographic process, depending on the mask
pattern.
[0049] In the chemical etching of the Al-SiC or Al-Si composite
material, the Al component is selectively etched. As the etching of
the Al component proceeds, and then SiC or Si particles are
removed. These mechanisms are repeated during the etching. Al,
which is amphoteric metal, can be etched with an acid or alkali.
Examples of etchants include acids, i.e., sulfuric acid, nitric
acid, and hydrochloric acid; and alkalis, i.e., sodium hydroxide.
In view of process control and handling, the etchant is preferably
in the form of an aqueous solution, but may be gaseous, for
example, hydrogen chloride gas.
[0050] In an aqueous acidic or alkaline etchant solution, the
concentration of the etchant is preferably controlled to 3 to 50
percent by mass in terms of a desired etching time (for example, 10
to 1,000 seconds). The chemical etching is generally performed at
room temperature and may be performed at higher temperature when
the etchant content is low or when a week etchant is used. When a
gaseous etchant is used, the surfaces of the composite material are
preferably heated during etching.
[0051] The first etching step should be performed at a high etching
rate since the recess is formed on a main face of the composite
material by etching Al and removing SiC or Si particles. Thus, the
etchant content in the aqueous acid or alkaline etchant solution is
in the range of 30 to 50 percent by mass. On the other hand, in the
second etching step, the etchant content in the aqueous etchant
solution is in the range of 3 to 30 percent by mass, and preferably
3 to 10 percent by mass so that Al is moderately removed, since the
roughness of the main faces is adjusted by etching of Al and
removal of hard particles is not essential.
[0052] In order to adjust etching rate, the etchant solution may
contain an etchant such as salts or chloride of metals nobler than
Al; for example, copper sulfate (CuSO.sub.4), by 50 mass percent or
more of the total etchants. In the case where such metal salt or
chloride etchant is added in an aqueous etchant solution, the total
etchant content is preferably in the range of 3 to 50 percent by
mass, that is, the total etchant content is preferably somewhat
higher than in the case where such metal salt or chloride etchant
is not added. Alternatively, a chemical substance having the
inverted property to the aqueous etchant solution (an alkaline
substance for an acidic etchant solution or an acidic substance for
an alkaline etchant solution) may be added to form a metal salt by
the reaction of the chemical substance and the etchant.
[0053] In the second etching process, preferably, etching
parameters such as etchant content and etching time are
preliminarily determined by experiments to form a desired surface
profile. For example, in the case of an Al-SiC(20%) composite
material prepared by a casting method, desired surface unevenness
can be obtained by etching at 40.degree. C. for 30 to 120 seconds
with an aqueous solution containing a 5 mass percent NaOH etchant
or at 20.degree. C. for 40 to 180 seconds in an aqueous solution
containing a 20 mass percent NaOH etchant. FIG. 5 is a graph of a
surface unevenness profile when the Al-SiC(20%) composite material
is etched at 40.degree. C. for 60 seconds in the aqueous solution
containing 5 mass percent NaOH etchant.
[0054] Because powdered Al, SiC, and Si inevitably contain oxygen
at their surfaces, each of the composite materials prepared by
high-temperature treatment of these powdered raw materials has an
ultra-thin layer of Al or Si oxide or Al silicate at its surface.
It is preferable to remove the oxide or silicate layer since the
layer reduces bonding strength of the heat-dissipating substrate to
other components and increases thermal resistance at the surface of
the heat-dissipating substrate. In order to remove the surface
oxide or silicate layer, the liquid or gaseous etchant preferably
contain a trace amount of hydrogen fluoride (HF) However, if the
etchant in the second etching step contains 1 percent by mass or
more of HF, it is difficult to obtain a desired surface profile
(roughness).
[0055] In the first and second etching steps, individual composite
materials may be independently etched. Alternatively, an array of
composite materials may be simultaneously etched. In this method, a
plurality of heat-dissipating substrates can be prepared by one
etching operation. For example, as shown in FIG. 2, an array of
composite materials for preparing a plurality of heat-dissipating
substrates 10 is provided. In the first etching step, the recess 11
of each heat-dissipating substrate 10 is formed, allowing a frame
13 to be left with a small thickness around the portions that are
to become the individual heat-dissipating substrates 10. Then, the
two main faces are subjected to the second etching step except for
the recess 11. Thus, a number of heat-dissipating substrates 10 can
be obtained simultaneously by removing the frame 13.
[0056] In the first etching step, Al is selectively etched while
SiC, Si, or SiC-Si particles are removed from the composite
material and a recess for mounting a semiconductor device and the
like is formed in any shape efficiently with high accuracy. The
recess formed in the first etching step is charcoal gray. This
color is probably due to the rough surface formed by detachment of
many particles, where the amplitude of the surface roughness in the
depth direction is larger than the maximum length of the particles
in the depth direction.
[0057] In the first etching step, the mass ratio of the first
composition primarily composed of Al and the size of the SiC, Si,
or SiC-Si particles have an effect on the entire shape of the
etched substrate. That is, if the first composition is 55 percent
by mass or more and the average particle size of the particles such
as SiC is in the range of 5 to 40 .mu.m and preferably 10 to 20
.mu.m, the curvature of the resulting heat-dissipating substrate in
the thickness direction can be suppressed to 0.08 mm or less even
if the heat-dissipating substrate is thin. When the mass ratio or
particle size of the first composition is out of the above ranges,
the etching rate decreases such that much time is needed for
forming the recess. It is likely that the substrate is unevenly
etched and local deformation of the substrate is accelerated during
the long etching time.
[0058] The composite material for the heat-dissipating substrate is
charcoal gray with Al metallic luster when it is prepared by the
infiltration process, the sintering process, or the casting
process. In the second etching step, the main faces of the
composite material become gray or light gray and do not have
metallic luster. This is because that the maximum amplitude of fine
unevenness on the main faces in the depth direction is smaller than
the maximum length of hard particles exposed at the main faces in
the depth direction. Thus, a product name and lot number can be
printed on the main face by laser irradiation or with black ink so
as to be clearly identified.
[0059] The joint frame surrounding the recess of the main face also
has fine unevenness exhibiting the same characteristics after the
second etching step. Moreover, as described above, the
heat-dissipating substrate has a small curvature in the thickness
direction; hence, the joint frame has high bonding strength for
connection with other components, whereby a highly reliable package
can be obtained.
[0060] The surface roughness achieved by the second etching step of
the two main faces excluding the recess is preferably in the range
of 0.2 to 2 .mu.m in terms of Ra according to JIS B 0651. A surface
with a roughness Ra of less than 0.2 .mu.m has metallic luster,
which impairs visibility of the printed letters, and tends to
decrease bonding strength for connection with other components.
[0061] Also, a rough surface with a roughness Ra exceeding 2 .mu.m
impairs visibility of the printed letters.
[0062] Such a surface roughness may be formed by a combination of
the second etching step with any of surface finishing steps such as
sand blasting and barrel polishing or with a rolling step using
rollers having fine unevenness.
[0063] The additional step is preferably performed after the second
etching step; however, such a combination may readily form a
curvature over the entire heat-dissipating substrate in the case of
a thin heat-dissipating substrate with a maximum thickness of 2.0
mm or less. In such a case, the curvature is larger than 0.08 mm in
the thickness direction, for example.
[0064] In contrast, in the case of a heat-dissipating substrate
prepared by the first and second etching steps according to the
present invention, the curvature can be suppressed to 0.08 mm or
less even if the thickness of the heat-dissipating substrate is 2.0
mm or less. In particular, a curvature of 0.05 mm, which is a
requirement for commercial products, can be achieved for a thin
heat-dissipating substrate in which the ratio (t/A) of the maximum
thickness t (mm) between the two main faces to the area A
(mm.sup.2) of a main face is 0.002 (mm.sup.-1) or less.
[0065] The present invention further provides a semiconductor
device (including a package) using a heat-dissipating substrate
which is produced by the first and second etching steps and which
has a recess in a main face, wherein the main faces excluding the
recess have fine unevenness (specific surface roughness).
EXAMPLE 1
[0066] For the first composition, powders each including Al whose
purity is 99.4 mass percent and whose average particle size is
40.mu. were prepared: a pure Al powder (Al Powder 1), an atomized
Al alloy powder containing 5 percent by mass of Si (Al Powder 2),
and an atomized Al alloy powder containing 5 percent by mass of Mg
(Al Powder 3). For the second composition, SiC and Si powders, each
having a purity of 99.8 percent by mass and an average particle
size shown in Table II were prepared.
[0067] These powders were mixed according to the composition for
the composite material shown in Table II, and each mixture was
molded into a square planar green compact with a length (width) of
50 mm and a thickness of 10 mm. The green compacts were heated to
665.degree. C. in a belt furnace of a nitrogen atmosphere and held
at the temperature for 30 minutes for sintering to obtain composite
materials, which were each hot-rolled into a sheet of 1.0 mm in
thickness.
2 TABLE II Composition of Composite Material Second Composition
Sample First Composition SiC Si Average Particle Size (.mu.m) 1 Al
Powder 1:53 -- 47 15 2 Al Powder 1:55 -- 45 15 3 Al Powder 1:70 --
30 15 4 Al Powder 1:80 -- 20 15 5 Al Powder 1:88 -- 12 15 6 Al
Powder 1:96 -- 4 15 7 Al Powder 1:53 47 -- 15 8 Al Powder 1:55 45
-- 15 9 Al Powder 1:60 40 -- 15 10 Al Powder 1:80 20 -- 15 11 Al
Powder 1:95 5 -- 15 12 Al Powder 1:96 4 -- 15 13 Al Powder 1:80 20
-- 3 14 Al Powder 1:80 20 -- 5 15 Al Powder 1:80 20 -- 10 16 Al
Powder 1:80 20 -- 20 17 Al Powder 1:80 20 -- 25 18 Al Powder 1:80
20 -- 40 19 Al Powder 1:80 20 -- 43 20 Al Powder 1:60 30 10 15 21
Al Powder 1:70 22 8 15 22 Al Powder 1:80 15 5 15 23 Al Powder 2:55
45 -- 15 24 Al Powder 2:70 30 -- 15 25 Al Powder 2:80 20 -- 15 26
Al Powder 2:95 5 -- 15 27 Al Powder 3:80 20 -- 15
[0068] Each resulting composite material sheet had a charcoal gray
surface with metallic luster. The metallic luster tended to
increase according to the increase in the ratio of the first
composition. The surface roughness Ra of each composite material
sheet was measured. A cut piece was prepared from the composite
material sheet, and the thermal conductivity and the thermal
expansion coefficient of each cut piece were measured by a laser
flash method and a differential transformer, respectively. These
results are shown in the column "Properties of Unetched Composite
Material" in Table III.
[0069] Each composite material sheet was immersed into an aqueous
10 mass percent NaOH solution at 30.degree. C. for 60 seconds to
etch the surfaces of the composite material sheet (the second
chemical etching step). The surface roughness Ra of the etched
composite material sheet was measured and the surface color was
observed. The results are shown in the column "Properties of Etched
Composite Material" in Table III. The state of surfaces at this
stage corresponds to the surface roughness of the main faces
excluding the recess of the composite material according to the
present invention.
[0070] Each composite material sheet was subjected to chemical
etching (corresponding to the first etching step in the present
invention) along a pattern shown by dotted lines in FIG. 2 to
separate heat-dissipating substrates 10 and to form a recess 11 on
each heat-dissipating substrate 10. More specifically, after a
surface of the composite material sheet, except for portions
corresponding to the recesses 1, was masked by a photolithographic
process, the sheet was immersed in an aqueous 30 mass percent NaOH
solution at 30.degree. C. for 30 to 60 seconds to form the square
recesses 11 with a length (width) of 15 mm and a depth of 0.5 mm.
Next, portions other than the frame 13 were masked in the same
manner, and the sheet was immersed in the same NaOH solution at
30.degree. C. for 30 to 60 seconds for etching.
[0071] In all of the twelve lid-type heat-dissipating substrates
thus prepared, each recess was charcoal gray, whereas other
portions of the faces were gray or light gray without metallic
luster as shown in Table III, so that letters printed on the faces
by laser irradiation or with black ink were easily readable. Each
heat-dissipating substrate had a length (width) of 30 mm, a maximum
thickness of 1 mm, and a thickness at the recess of 0.5 mm.
[0072] The curvature of each heat-dissipating substrate was
measured. The results are shown in the column "Properties of Etched
Composite Material" in Table III. The measurement of curvature was
performed as shown in FIG. 6. More specifically, the
heat-dissipating substrate 20 was placed on a platen 21, putting
the main face having the recess downward, and a laser beam 22a was
emitted from a laser light source 22 to scan along two diagonal
lines of the main faces on the upper side so as to measure the
distance from the light source 22 to the main face. The curvature
was defined as larger one of the ratios (L.sub.0-L)/D calculated
for the two diagonal lines, where the scanning distance in each
diagonal line was D (mm) and the minimum distance and maximum
distance from the light source 22 to the main face were L (mm) and
L.sub.0 (mm), respectively.
[0073] Using the above-described hot-rolled sheets with a thickness
of 1 mm, samples having a length (width) of 30 mm and a thickness
of 1 mm were prepared in the same quantity as in Table III by
mechanical cutting and polishing, and then the recess portion and
main faces thereof were subjected to etching under the same
conditions as in the above chemical etching steps. The curvature of
theses samples was also measured. The curvature of all the samples
exceeded 1.0 mm.
[0074] Each heat-dissipating substrate was subjected to 500
cooling/heating cycles, each cycle consisting of holding the sample
at -60.degree. C. for 30 minutes and then at +150.degree. C. for 30
minutes. Then, the curvature of the heat-dissipating substrate was
measured in the same manner as described above. The curvature of
the heat-dissipating substrate according to the present invention
did not substantially change by this cooling/heating cycles.
3 TABLE III Properties of Unetched Composite Material Properties of
Etched Thermal Composite Material Thermal Expansion Surface Surface
Conductivity Coefficient Roughness Roughness Curvature Sample (W/m
.multidot. K) (.times.10.sup.-6/.degree. C.) Ra (.mu.m) Ra (.mu.m)
(mm) Surface Color 1 180 14.5 0.2 1.2 0.07 light gray 2 182 14.9
0.2 1.0 0.05 3 190 18.0 0.15 0.9 0.05 4 200 18.5 0.15 0.9 0.05 5
208 19.3 0.15 0.9 0.04 6 214 21.0 0.17 1.2 0.03 light gray (slight
luster) 7 263 14.2 0.2 1.2 0.07 light gray 8 260 15.0 0.2 1.2 0.06
9 253 16.0 0.15 1.0 0.04 10 235 20.0 0.15 1.0 0.03 11 224 23.0 0.17
1.1 0.03 12 221 23.5 0.17 1.1 0.03 light gray 13 232 19.8 0.1 0.9
0.06 (slight luster) 14 234 19.8 0.1 0.9 0.05 light gray 15 235
20.0 0.15 1.0 0.02 16 236 20.0 0.15 1.0 0.02 17 236 20.2 0.16 1.5
0.04 gray 18 237 20.4 0.2 1.6 0.04 19 238 20.5 0.2 1.7 0.06
charcoal gray 20 178 15.4 0.15 1.1 0.05 light gray 21 237 18.4 0.15
1.0 0.04 22 228 20.3 0.15 1.0 0.04 23 214 13.0 0.1 1.0 0.02 24 206
14.6 0.15 0.9 0.03 25 202 17.5 0.15 0.9 0.03 26 194 22.0 0.2 1.0
0.03 27 198 16.0 0.13 0.8 0.03
EXAMPLE 2
[0075] Using the same powders as those in EXAMPLE 1, composite
materials having the compositions shown in Table II were prepared
by a casting process. That is, a powder of the first composition
was melt at 680.degree. C. in a nitrogen atmosphere, and a SiC or
Si powder of the second composition was added to the melt and
thoroughly mixed to be dispersed into the melt. Then, the melt was
cast into a mold having dimensions of 200 mm.times.100 mm.times.20
mm and cooled to produce a composite material. The composite
material was rolled into a sheet with a thickness of 2.0 mm as in
EXAMPLE 1.
[0076] Each of the resulting composite material sheets had charcoal
gray surfaces with metallic luster. The metallic luster became
noticeable as the first composition content increased. The density
of each sheet was almost the same as that in EXAMPLE 1. The thermal
conductivity of each sheet was slightly (up to about 8%) lower than
that of the corresponding sheet by the sintering process shown in
Tables II and III, while the thermal expansion coefficient was
slightly (up to about 5%) higher than that of the corresponding
sheet by the sintering process.
[0077] Each composite material sheet was immersed into an aqueous
10 mass percent NaOH solution as in EXAMPLE 1 (the second chemical
etching step). The etched faces were gray or light gray without
metallic luster, so that letters printed on the faces were easily
readable.
[0078] Each sheet of the composite material had a size of about 200
mm.times.1,000 mm.times.2 mm. The sheet was masked such that 180
square substrates, each having a length (width) of 30 mm and a
thickness of 2 mm, were produced. The sheet was subjected to
chemical etching as in EXAMPLE 1 to separate the 180 lid-type
heat-dissipating substrates and to form a square recess with a
length (width) of 15 mm and a depth of 1 mm on each
heat-dissipating substrate. Some of these heat-dissipating
substrates were subjected to measurement of the curvature before
and after the cooling/heating cycles described in EXAMPLE 1. The
curvature was substantially the same as that shown in Tables II and
III and was substantially not affected by the cooling/heating
cycles.
EXAMPLE 3
[0079] Composite materials with a length (width) of 30 mm and a
thickness of 1.0 mm having the same composition as that of Sample
10 of Table II in EXAMPLE 1 were prepared by the sintering and
rolling methods described in EXAMPLE 1, and the relationship
between the surface roughness and chemical etching conditions was
investigated. The chemical etching conditions were varied as shown
in Table IV. The surface color of each etched sample was observed
and the surface roughness Ra of each sample was measured. These
results are shown in Table V. The surfaces of the unetched
composite materials of Sample 10 were charcoal gray with metallic
luster.
4TABLE IV Etching Time Sample Etchant Composition (percent by mass)
(min) 10-1 8% H.sub.2SO.sub.4 aqueous solution 30 10-2 10%
H.sub.2SO.sub.4 aqueous solution 30 10-3 15% H.sub.2SO.sub.4
aqueous solution 30 10-4 12% H.sub.2SO.sub.4 + 12% CuSO.sub.4
aqueous solution 30 10-5 32% H.sub.2SO.sub.4 aqueous solution 30
10-6 8% HNO.sub.3 aqueous solution 30 10-7 8% HNO.sub.3 + 0.7% HF
aqueous solution 10 10-8 8% HNO.sub.3 + 0.4% HF aqueous solution 10
10-9 8% NaOH aqueous solution 30 10-10 10% NaOH aqueous solution 30
10-11 15% NaOH aqueous solution 30 10-12 32% NaOH aqueous solution
30 10-13 12% NaOH + 12% CuSO.sub.4 aqueous solution 30 10-14 48%
H.sub.2SO.sub.4 aqueous solution 3 10-15 52% H.sub.2SO.sub.4
aqueous solution 3
[0080] Each etched composite material with a length and width of 30
mm and a thickness of 1.0 mm was subjected to chemical etching to
form a recess as in EXAMPLE 1.The resulting heat-dissipating
substrates were evaluated with respect to their properties for
bonding with a semiconductor device component.
[0081] Test pieces A having a recess on a main face thereof and an
Au-Sn solder metallized layer on the other main face thereof were
prepared. A copper wire of 1 mm in diameter was perpendicularly
fixed to the main face of each test piece through a semispherical
Al-Sn solder layer formed thereon with a diameter of 5 mm. With
each of the five test pieces A thus prepared, evaluation as to
whether or not the copper wire was detached from the substrate was
done in a manner in which the copper wire was pulled upward at a
rate of 5 mm/sec in a direction perpendicular to the substrate and
such state was maintained for 15 minutes while each substrate was
fixed. As a result, none of the copper wires were detached from any
substrates. However, minute cracks were found in the metallized
layer of Sample 10-15.
[0082] Test pieces B (package) were prepared, in which a substrate
was provided with a recess on its main face and a tungsten
metallized layer and a nickel plate layer were formed on the main
face, and laminated circuits having the same size as the substrate
(width and length: 30 mm.times.30 mm) were bonded on top of these
layers through an Au-Sn solder, wherein the laminated circuits were
composed of five aluminum nitride ceramic layers on each of which a
tungsten pattern circuit is formed. Each of the test pieces B was
subjected to cooling/heating cycles as in EXAMPLE 1 and the
curvature thereof was measured before and after the cooling/heating
cycles as described in EXAMPLE 1 and FIG. 6. The results are shown
in Table V.
5 TABLE V Curvature After Etching Before After Sample Surface Color
Ra (.mu.m) Heat cycles Heat cycles 10-1 light gray 0.5 0.03 0.03
10-2 light gray 0.8 0.03 0.03 10-3 gray 1.6 0.05 0.06 10-4 light
gray 0.7 0.02 0.02 10-5 gray 1.8 0.06 0.06 10-6 light gray 0.6 0.03
0.03 10-7 gray 1.7 0.05 0.06 10-8 light gray 1.0 0.03 0.03 10-9
light gray 0.6 0.03 0.03 10-10 light gray 0.8 0.03 0.03 10-11 gray
1.5 0.05 0.05 10-12 gray 2.0 0.05 0.05 10-13 light gray 2.0 0.02
0.02 10-14 light gray 1.9 0.06 0.08 10-15 slightly dark gray 2.4
0.09 0.12
[0083] The above results demonstrate that the surface of the
substrate is gray or light gray suitable for identification of
printed letters when the etchant content in the second chemical
etching step is 30 percent by mass or less. When the etchant
content is 10 percent by mass or less, the surface is light gray
more suitable for identification of printed letters.
[0084] By adding a salt of a nobler metal than Al to the aqueous
acidic or alkaline etchant solution, a light gray surface is
obtainable even if the acid or alkali content exceeds 10 percent by
mass. Addition of 0.5 percent by mass of HF to the sulfuric acid
solution reduces the etching time.
EXAMPLE 4
[0085] According to the same compositions as those in Samples 4 and
9 in Table II in EXAMPLE 1, composite material sheets with various
thicknesses shown in Table VI were prepared by the sintering and
rolling processes shown in EXAMPLE 1. Each composite material sheet
was immersed in an aqueous 10 mass percent NaOH solution to control
surface roughness (the second chemical etching step according to
the invention) under the same conditions as those in EXAMPLE 1.
Subsequently, each composite material sheet was subjected to
chemical etching (the first etching step in the present invention)
using an aqueous 30 mass percent NaOH solution as in EXAMPLE 1 to
separate substrates and to form a recess in a main face of each
substrate. Thus, heat-dissipating substrates having a length
(width) of 30 mm (main face area (A): 900 mm.sup.2) were produced
in various thickness (t).
[0086] After that, a tungsten metallized layer and a nickel plate
layer were formed on the main face opposite to a main face having a
recess, and laminated circuits composed of five aluminum nitride
ceramic layers each having a tungsten pattern circuit were bonded
onto these layers with an Au-Sn solder. Each test piece thus
prepared was subjected to cooling/heating cycles as in EXAMPLE 1
and the curvature was measured before and after the cooling/heating
cycles by the method shown in FIG. 6 and EXAMPLE 1. The results are
shown in Table VI in which t/A denotes the rate of the maximum
thickness t (mm) between the two main faces to the area A (900
mm.sup.2) of a main face.
[0087] As shown in Table VI, the curvature was not increased by the
cooling/heating cycles, although after etching it slightly
increased when the substrate thickness was 1.5 mm or less and when
the t/A was less than 0.002; however, such curvature does not cause
any problem for practical use. Furthermore, an evaluation was done
in the same manner as described above using composite material
samples prepared by the casting method described in EXAMPLE 2. The
results were substantially the same as those shown in Table VI.
6 TABLE VI Curvature (mm) Before After Thickness Depth of Heat Heat
Sample t (mm) t/A (mm2) Recess (mm) cycles Cycles Sample 4 in 1.0
0.0011 0.5 0.04 0.04 Table II 1.5 0.0017 0.8 0.04 0.04 1.8 0.0020
0.9 0.03 0.03 2.0 0.0022 1.0 0.03 0.03 Sample 9 in 1.0 0.0011 0.5
0.04 0.04 Table II 1.5 0.0017 0.8 0.04 0.04 1.8 0.0020 0.9 0.03
0.03 2.0 0.0022 1.0 0.03 0.03
EXAMPLE 5
[0088] Composite material sheets were prepared according to ten
kinds of compositions for Samples 2 to 5, 8 to 11, and 24 to 25 in
Table II in EXAMPLE 1 by means of the sintering method used in
EXAMPLE 1 and the casting method used in EXAMPLE 2. These composite
material sheets were subjected to the same chemical etching
processes, and heat-dissipating substrates were prepared which had
a length (width) of 30 mm and a thickness of 1 mm, each having a
square recess with a length (width) of 15 mm and a depth of 0.5 mm
on a main face thereof. The main faces having a recess of these
substrates were bonded respectively to aluminum nitride laminated
circuits having a length (width) of 30 mm in the same manner as
described in EXAMPLE 4 and thereby packages were fabricated,
respectively.
[0089] Each package was subjected to 1,000 cooling/heating cycles
in the same manner as described in EXAMPLE 1, and the curvature of
the substrate was measured before and after the cooling/heating
cycles with respect to its main face opposite to the main face
having a recess, and the bonding portion connected to the laminated
circuits was observed by a microscopic view to evaluate any
occurrence of damage after the cooling/heating cycles. As a result,
there was neither recognizable change in curvature nor damage to
the bonding portion with respect to all the samples. Accordingly,
the semiconductor device using the heat-dissipating substrate
according to the present invention is highly reliable.
* * * * *